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Unformatted text preview: AP1200 Foundation Physics Limited wisdom and incorrect predictions: "So we went to Atari and said, 'Hey, we've got this amazing thing, even built with some of your parts, and what do you think about funding us? Or we'll give it to you. We just want to do it. Pay our salary, we'll come work for you.' And they said, 'No.' So then we went to Hewlett-Packard, and they said, 'Hey, we don't need you. You haven't got through college yet."' -- Apple Computer Inc. founder Steve Jobs on attempts to get Atari and H-P interested in his and Steve Wozniak's personal computer. "I think there is a world market for maybe five computers." -- Thomas J. Watson, Chairman of IBM, 1943. "Computers in the future may weigh no more than 1.5 tons." -- Popular Mechanics, forecasting the [unstoppable] march of science, 1949. "I have travelled the length and breadth of this country and talked with the best people, and I can assure you that data processing is a [fashion] that won't last out the year." -- The editor in charge of business books for Prentice Hall, 1957. "There is no reason anyone would want a computer in their home." -- Ken Olson, president, chairman and founder of Digital Equipment Corp., 1977 Chapter 6: Magnetism The compass was used in China as early as 3700 years ago. The Greeks discovered that some rocks attract pieces of iron 2800 years ago. Magnets have a north and a south pole, similar to the positive and negative charges of electric forces. Opposite poles (N-S) attract each other, but like poles (N-N or S-S) repel each other. However, different from electric charges, magnetic poles always come in pairs (N+S): single magnetic poles (often called monopoles) have not been observed in nature. If you cut a magnet into 2 pieces, each piece will still have a north and a south pole. The combination of a north pole and a south pole is called a magnetic dipole (analogous to the combination of a positive charge and a negative charge called an electric dipole). Early in the 19 th century, scientists realized there was a connection between electricity and magnetism. A changing magnetic field creates an electric field. Similarly, a changing electric field creates a magnetic field. We have seen that electric fields surround an electrically charged particle, whether it moves or not. By contrast, magnetic fields are created when a charge moves . A magnetic field also surrounds a magnetic substance such as a permanent magnet. 1 6.1 Magnetic Fields and Forces The symbol B r is used to represent a magnetic field. As with electric fields, we can represent magnetic fields using field lines. Magnets align themselves with the magnetic field B r , so small magnets can be used to trace out magnetic fields (Fig. 6.1). Field lines point away from north poles and toward south poles....
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- Spring '10